This application is claiming priority to Great Britain Patent application No. 0005886.7 filed Mar. 13, 2000.
The present invention relates to apparatus for electro-plating and to a method of electro-plating.
A major problem associated with electro-plating, especially when high deposition rates are attempted, is the irregularity of deposition.
Another major problem is the need for all areas that are to be plated to be electrically connected.
To obtain a uniform plating deposit using existing methods, the required situation is that given by two parallel, co-axial and equi-potential conducting planes separated by a medium of homogenous resistance. If a potential difference exists between the two planes, then the current will flow between and normal to the two planes with uniform density (see FIG. 1). If the medium separating the two planes is an electrolyte of suitable composition containing adequate, and suitable ions of the material to be deposited, then a uniform deposition of the material will be made on the plane which is at the more negative potential. The amount of the deposit is dependent upon the material type and the total electrical charge.
In practice, the situation described above does not occur, due to surface roughness of the two planes and the lack of homogeneity of the electrolyte. Also, practical difficulties, associated with achieving true parallelism of the planes and the possible irregular pattern of the conductive surface of the negative (target) plane and the restrictions of the electrolyte flow, to some or all of the target plane surface, add to the lack of uniformity of the current density within the electrolyte. This results in irregular deposits of material on the target surface.
FIG. 2 shows the distortion of the current stream, and therefore current density distribution, due to the irregularity of the target (negative) surface. Further distortions due to the irregularities in the positive surface and variations in the electrolyte resistance are not shown.
FIG. 3 shows the accentuation of the irregularities in the target surface due to the unequal current density distribution. The interaction of unequal current density and surface irregularity can be seen to be mutually progressive.
Several techniques have been employed to offset these effects including the use of current diversions (robber bars) at the target surface. Such techniques are only partially successful and are inherently inefficient. There are few, if any, practical techniques for dealing with situations in which the target surface has areas which are to be plated but which are not electrically connected.
The present invention comprises electro-plating apparatus having means to direct electrolyte to a target, and means to control the amount of reduction, and/or rate thereof, of ions in the selected regions of the target.
The electro-plating apparatus may comprise means to monitor the current flow in some or all regions of the target.
The electro-plating apparatus may comprise means to regulate the current flow to each region so that the material deposition rate for each region may be independently varied.
The direction as may comprise a hollow, elongate, body along the interior of which electrolyte passes (e.g. by pumping, or other pressurising methods, or other methods for inducing flow) for exit through an outlet and towards a target being a substrate maintained at a negative voltage relative to part of the body, whereby the target forms a cathode and the part of the body forms an anode. The anode part of the body may be formed of a single element or of a plurality of electrically isolated elements or rods. In a particular, advantageous embodiment, the direction means comprises a plurality of hollow tubes for the flow of electrolyte along the interior of the tubes and towards the target.
Electro-plating apparatus may include any one or more of the following features:
the control means comprises means to regulate the current applied to each of a plurality of separate regions of the target.
the control means comprises means to regulate the size and/or duration of current applied to each of a plurality of separate regions of the target.
the control means comprises means to measure the current flowing to a region of the target and means to control the current applied to that region in dependence on the output of the measurement means.
control means operable to provide a reduction layer of uniform thickness on the target.
control means operable to provide a reduction layer on the target wherein different regions have predetermined reduction thicknesses.
control means operable to provide a target with a uniform reduction thickness in selected regions.
the control means comprises means to control the current flow to each region so that the ion reduction rate for each region may be independently varied.
the control means comprises means to monitor the current flow in all regions of the target.
the direction means comprises a hollow, elongate body for the passage of electrolyte along the interior of the body.
a single element anode.
an anode formed of a plurality of generally parallel solid rods.
an anode formed of a plurality of generally parallel tubes through which electrolyte passes.
means to effect swirling of the electrolyte in the vicinity of contact with the target.
swirling means comprises shaping of the body and/or the outlet such that the vortices are created or enhanced.
serrations in the leading edge of the anode.
The electro-plating apparatus may comprise means to effect movement of the electrolyte in the region of contact with the target, thereby to enhance impingement between electrolyte and target to optimise ion availability. In one embodiment, the shape of the body and the outlet are such that swirling is created or enhanced, typically by the inclusion of serrations in the leading edge of the anode.
The present invention comprises a method of electro-plating comprising directing electrolyte to a target and controlling the amount of deposition, and/or rate thereof, of material in selected regions of the target.
The method may comprise monitoring the current flow in some or all regions of the target.
The method may comprise regulating the current flow to each region so that the material deposition rate for each region may be independently varied.
The method may comprise effecting movement of the electrolyte in the region of contact with the target, thereby to enhance impingement between electrolyte and target to optimise ion availability. In one embodiment, the shape of the body and the outlet are such that swirling is created or enhanced, typically by the inclusion of serrations in the leading edge of the anode.
The present invention also provides a computer program product directly loadable into the internal memory of a digital computer, comprising software code portions for performing the steps of a method according to the present invention, when said product is ran on a computer.
The present invention also provides a computer program product stored on a computer useable medium, comprising:
computer readable program means for causing the computer to control the amount of deposition, and/or rate thereof, of material in selected regions of the target.
The present invention also provides electronic distribution of a computer program as defined in the present invention.